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The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

Identification: Bythotrephes longimanus is a large cladoceran distinguished by a long straight tail spine that is twice as long as its body and has one to three pairs of barbs. Parthenogenically produced animals have kink in middle of their spine and sexually produced animals lack the kink. Bythotrephes' appearance is similar to Cercopagis pengoi, another Great Lakes invader, except Bythotrephes is larger with a more robust spine that lacks a hook at the end.

Table 1. States with nonindigenous occurrences, the earliest and latest observations in each state, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Bythotrephes longimanus are found here.

Ecology: Bythotrephes is found among the zooplankton in the upper water column of large and small temperate lakes, can tolerate brackish water, and is most abundant in late summer and autumn. Occurrence and density of Bythotrephes populations are apparently determined mainly by water temperature and salinity. Bythotrephes is limited to regions where water temperature ranges between 4 and 30°C and salinity values between 0.04 and 8.0‰, but it prefers temperature between 10 and 24°C and salinity between 0.04 and 0.4‰ (Grigorovich et al. 1998). Temperature appears to play a major role in determining the abundance and location of Bythotrephes in the Great Lakes, as it prefers cooler water and cannot tolerate very warm lake temperatures (Berg and Garton 1988, Garton et al. 1990, Brown and Branstrator 2004). Bythotrephes occurs in oligotrophic and mesotrophic lakes and has a lower tolerance to low dissolved oxygen concentrations than the native cladoceran Leptodora kindtii (Sorensen and Branstrator 2017). Bythotrephes can reproduce asexually as well as sexually; unfertilized eggs are carried in a brood pouch, and fertilized eggs are cast in the fall, hatching the following spring (Evans 1988). The intensity and type of predation pressure appears to affect the size of Bythotrephes, its spine length, and the extent of its diel migrations (Straile and Halbich 2000).

Status: Bythotrephes is established in all of the Great Lakes and many inland lakes in the region. Densities are very low in Lake Ontario, low in southern Lake Michigan and offshore areas of Lake Superior, moderate to high in Lake Huron, and very high in the central basin of Lake Erie (Barbiero et al. 2001, Vanderploeg et al. 2002, Brown and Branstrator 2004).

Impact of Introduction: It has caused major changes in the zooplankton community structure; invasion history; reproduce rapidly; competes directly with small fish and can have impact on zooplankton community (USEPA 2008).

The first noticeable impact of Bythotrephes was on fisherman. The tail spines of Bythotrephes hook on fishing lines, fouling fishing gear. Bythotrephes consumes small zooplankton such as small cladocerans, copepods, and rotifers, competing directly with planktivorous larval fish for food (Berg and Garton 1988, Evans 1988, Vanderploeg et al. 1993). Bythotrephes has been implicated as a factor in the decline of alewife (Alosa pseudoharengus) in Lakes Ontario, Erie, Huron, and Michigan (Evans 1988). Bythotrephes also competes with, and possibly preys on, Leptodora kindtii and may be a causal factor in the decline of Leptodora (Branstrator 1995). Bythotrephes and Leptodora abundances are often negatively correlated (Garton et al. 1990, Branstrator 1995). There is speculation that Bythotrephes may control the abundance of Cercopagis pengoi though competition and predation (Vanderploeg et al. 2002). Bythotrephes is a food source for fish including yellow perch, white perch, walleye, white bass, alewife, bloater chub, chinook salmon, emerald shiner, spottail shiner, rainbow smelt, lake herring, lake whitefish and deepwater sculpin (Bur et al. 1986, Makarewicz and Jones 1990, Branstrator and Lehman 1996).

Barbiero, R.P., R.E. Little, and M.L. Tuchman. 2001. Results from the US EPA's biological open water surveillance program of the Laurentian Great Lakes: III. Crustacean zooplankton. Journal of Great Lakes Research 27:167-184.

Barbiero, R.P. and D.C. Rockwell. 2008. Changes in the crustacean communities of the central basin of Lake Erie during the first full year of the Bythotrephes longimanus invasion. Journal of Great Lakes Research 34(1):109-121.

Barbiero, R.P. and M.L. Tuchman. 2004. Changes in the crustacean communities of Lakes Michigan, Huron, and Erie following the invasion of the predatory cladoceran Bythotrephes longimanus. Canadian Journal of Fisheries and Aquatic Sciences 61:2111-2125.

Barbiero, R.P. and G.J. Warren. 2011. Rotifer communities in the Laurentian Great Lakes, 1983-2006 and factors affecting their composition. Journal of Great Lakes Research 37(3): 528-540.

Berg, D.J., and D.W. Garton. 1988. Seasonal abundance of the exotic predatory cladoceran, Bythotrephes cederstroemi, in western Lake Erie. Journal of Great Lakes Research 14(4):479-488.

Berg, D.J., and D.W. Garton. 1994. Genetic differentiation in North American and European populations of the cladoceran Bythotrephes. Limnology and Oceanography 39:1503-1516.

Branstrator, D.K. 1995. Ecological interactions between Bythotrephes cederstroemi and Leptodora kindtii and the implications for species replacement in Lake Michigan. Journal of Great Lakes Research 21:670-679.

Branstrator, D.K., and J.T. Lehman. 1996. Evidence for predation by young-of-the-year alewife and bloater chub on Bythotrephes cederstroemi in Lake Michigan. Journal of Great Lakes Research 22:917-924.

Brown, M.E., and D.K. Branstrator. 2004. A 2001 survey of crustacean zooplankton in the western arm of Lake Superior. Journal of Great Lakes Research 30:1-8.

Pichlová-Ptácníková, R., and H.A. Vanderploeg. 2011. The quick and the dead: might differences in escape rates explain the changes in the zooplankton community composition of Lake Michigan after invasion by Bythotrephes? Biological Invasions 13(11):2595-2604.

Sorensen, M.L., and D.K. Branstrator. 2017. The North American invasive zooplanktivore Bythotrephes longimanus is less hypoxia-tolerant than the native Leptodora kindtii. Canadian Journal of Fisheries and Aquatic Sciences 74:824-832. http://dx.doi.org/10.1139/cjfas-2016-0188.

Sprules, W.G., H.P. Riessen, and E.H. Jin. 1990. Dynamics of the Bythotrephes invasion of the St. Lawrence Great Lakes. Journal of Great Lakes Research 16: 346-351.

Stewart, T.J., W.G. Sprules, and R. O’Gorman. 2009. Shifts in the diet of Lake Ontario alewife in response to ecosystem change. Journal of Great Lakes Research 35(2):241-249.

U.S. Environmental Protection Agency (USEPA). 2008. Predicting future introductions of nonindigenous species to the Great Lakes. National Center for Environmental Assessment, Washington, DC; EPA/600/R-08/066F. Available from the National Technical Information Service, Springfield, VA, and http://www.epa.gov/ncea.

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.

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